U.S. patent application number 16/347059 was filed with the patent office on 2020-03-05 for method for producing metal foam.
The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Jin Kyu LEE, Jong Min SHIN, Dong Woo YOO.
Application Number | 20200070248 16/347059 |
Document ID | / |
Family ID | 62241677 |
Filed Date | 2020-03-05 |
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United States Patent
Application |
20200070248 |
Kind Code |
A1 |
YOO; Dong Woo ; et
al. |
March 5, 2020 |
METHOD FOR PRODUCING METAL FOAM
Abstract
The present application provides a method for manufacturing a
metal foam. The present application can provide a method for
manufacturing a metal foam, which is capable of forming a metal
foam comprising uniformly formed pores and having excellent
mechanical properties as well as the desired porosity, and a metal
foam having the above characteristics. In addition, the present
application can provide a method capable of forming a metal foam in
which the above-mentioned physical properties are ensured, while
being in the form of a thin film or sheet, within a fast process
time, and such a metal foam.
Inventors: |
YOO; Dong Woo; (Daejeon,
KR) ; LEE; Jin Kyu; (Daejeon, KR) ; SHIN; Jong
Min; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Family ID: |
62241677 |
Appl. No.: |
16/347059 |
Filed: |
November 29, 2017 |
PCT Filed: |
November 29, 2017 |
PCT NO: |
PCT/KR2017/013732 |
371 Date: |
May 2, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0059 20130101;
C22C 1/08 20130101; B22F 3/105 20130101; B22F 1/0074 20130101; B22F
2304/10 20130101; B22F 3/1125 20130101; B22F 5/006 20130101; B22F
2003/1053 20130101 |
International
Class: |
B22F 3/11 20060101
B22F003/11; B22F 1/00 20060101 B22F001/00; B22F 3/105 20060101
B22F003/105; B22F 5/00 20060101 B22F005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2016 |
KR |
10-2016-0162153 |
Claims
1. A method for manufacturing a metal foam, the method comprising:
forming a green structure using a slurry comprising a metal
component comprising a conductive metal with relative magnetic
permeability of 90 or more, a first solvent having a first
dielectric constant of 20 or more, and a second solvent having a
second dielectric constant of 15 or less; and sintering the green
structure.
2. The method for manufacturing a metal foam according to claim 1,
wherein the conductive metal has a conductivity of 8 MS/m or more
at 20.degree. C.
3. The method for manufacturing a metal foam according to claim 1,
wherein the conductive metal is nickel, iron or cobalt.
4. The method for manufacturing a metal foam according to claim 1,
wherein the metal component comprises 30 wt % or more of the
conductive metal.
5. The method for manufacturing a metal foam according to claim 1,
wherein the conductive metal has an average particle diameter in a
range of 10 to 100 .mu.m.
6. The method for manufacturing a metal foam according to claim 1,
wherein a ratio of the first dielectric constant of the first
solvent to the second dielectric constant of the second solvent is
in a range of 5 to 100.
7. The method for manufacturing a metal foam according to claim 1,
wherein the first dielectric constant of the first solvent is in a
range of 20 to 100.
8. The method for manufacturing a metal foam according to claim 1,
wherein the first solvent is water, an alcohol, acetone,
N-methylpyrrolidine, N,N-dimethylformamide, acetonitrile,
dimethylacetamide, dimethyl sulfoxide or propylene carbonate.
9. The method for manufacturing a metal foam according to claim 1,
wherein the second dielectric constant of the second solvent is in
a range of 1 to 15.
10. The method for manufacturing a metal foam according to claim 1,
wherein the second solvent is an alkane, an alkyl ether, pyridine,
ethylene dichloride, dichlorobenzene, trifluoroacetic acid,
tetrahydrofuran, chlorobenzene, chloroform or toluene.
11. The method for manufacturing a metal foam according to claim 1,
wherein the slurry comprises 100 to 300 parts by weight of the
metal component relative to 100 parts by weight of a total weight
of the first and second solvents.
12. The method for manufacturing a metal foam according to claim 1,
wherein the slurry comprises 0.5 to 10 parts by weight of the
second solvent relative to 100 parts by weight of the first
solvent.
13. The method for manufacturing a metal foam according to claim 1,
wherein the slurry further comprises a binder.
14. The method for manufacturing a metal foam according to claim 1,
wherein the sintering of the green structure is performed by
applying an electromagnetic field to the green structure.
15. The method for manufacturing a metal foam according to claim
14, wherein applying the electromagnetic field comprises applying a
current in a range of 100 A to 1,000 A.
16. The method for manufacturing a metal foam according to claim
14, wherein applying the electromagnetic field comprises applying a
current having a frequency in a range of 100 kHz to 1,000 kHz.
17. The method for manufacturing a metal foam according to claim
14, wherein the electromagnetic field is applied for a time in a
range of 1 minute to 10 hours.
18. The method for manufacturing a metal foam according to claim 1,
wherein the metal foam is in the form of a film or sheet.
19. The method for manufacturing a metal foam according to claim
18, wherein the film or sheet has a thickness of 5,000 .mu.m or
less.
20. The method for manufacturing a metal foam according to claim 1,
wherein the first solvent is water or N-Methylpyrrolidone, and
wherein the second solvent is pentane, hexane, or ethyl ether.
Description
TECHNICAL FIELD
[0001] This application claims the benefit of priority based on
Korean Patent Application No. 10-2016-0162153 filed on Nov. 30,
2016, the disclosure of which is incorporated herein by reference
in its entirety.
[0002] The present application relates to a method for
manufacturing a metal foam and a metal foam.
BACKGROUND ART
[0003] Metal foams can be applied to various fields including
lightweight structures, transportation machines, building materials
or energy absorbing devices, and the like by having various and
useful properties such as lightweight properties, energy absorbing
properties, heat insulating properties, refractoriness or
environment-friendliness. In addition, metal foams not only have a
high specific surface area, but also can further improve the flow
of fluids, such as liquids and gases, or electrons, and thus can
also be usefully used by being applied in a substrate for a heat
exchanger, a catalyst, a sensor, an actuator, a secondary battery,
a gas diffusion layer (GDL) or a microfluidic flow controller, and
the like.
DISCLOSURE
Technical Problem
[0004] It is an object of the present invention to provide a method
capable of manufacturing a metal foam comprising pores uniformly
formed and having excellent mechanical strength as well as a
desired porosity.
Technical Solution
[0005] In the present application, the term metal foam or metal
skeleton means a porous structure comprising two or more metals as
a main component. Here, the metal as a main component means that
the proportion of the metal is 55 wt % or more, 60 wt % or more, 65
wt % or more, 70 wt % or more, 75 wt % or more, 80 wt % or more, 85
wt % or more, 90 wt % or more, or 95 wt % or more based on the
total weight of the metal foam or the metal skeleton. The upper
limit of the proportion of the metal contained as the main
component is not particularly limited and may be, for example, 100
wt %.
[0006] The term porous property may mean a case where porosity is
30% or more, 40% or more, 50% or more, 60% or more, 70% or more,
75% or more, or 80% or more. The upper limit of the porosity is not
particularly limited, and may be, for example, less than about
100%, about 99% or less, or about 98% or less or so. Here, the
porosity can be calculated in a known manner by calculating the
density of the metal foam or the like.
[0007] The method for manufacturing a metal foam of the present
application may comprise a step of sintering a green structure
comprising a metal component having metals. In the present
application, the term green structure means a structure before the
process performed to form the metal foam, such as the sintering
process, that is, a structure before the metal foam is formed. In
addition, even when the green structure is referred to as a porous
green structure, the structure is not necessarily porous per se,
and may be referred to as a porous green structure for convenience,
if it can finally form a metal foam, which is a porous metal
structure.
[0008] In the present application, the green structure may be
formed using a slurry containing at least a metal component, and
first and second solvents.
[0009] In one example, the metal component may comprise at least a
metal having appropriate relative magnetic permeability and
conductivity. According to one example of the present application,
the application of such a metal can ensure that when an induction
heating method to be described below is applied as the sintering,
the sintering according to the relevant method is smoothly carried
out.
[0010] For example, as the metal, a metal having a relative
magnetic permeability of 90 or more may be used. Here, the relative
magnetic permeability (.mu..sub.r) is a ratio (.mu./.mu..sub.0) of
the magnetic permeability (.mu.) of the relevant material to the
magnetic permeability (.mu..sub.0) in the vacuum. The metal used in
the present application may have a relative magnetic permeability
of 95 or more, 100 or more, 110 or more, 120 or more, 130 or more,
140 or more, 150 or more, 160 or more, 170 or more, 180 or more,
190 or more, 200 or more, 210 or more, 220 or more, 230 or more,
240 or more, 250 or more, 260 or more, 270 or more, 280 or more,
290 or more, 300 or more, 310 or more, 320 or more, 330 or more,
340 or more, 350 or more, 360 or more, 370 or more, 380 or more,
390 or more, 400 or more, 410 or more, 420 or more, 430 or more,
440 or more, 450 or more, 460 or more, 470 or more, 480 or more,
490 or more, 500 or more, 510 or more, 520 or more, 530 or more,
540 or more, 550 or more, 560 or more, 570 or more, 580 or more, or
590 or more. The upper limit of the relative magnetic permeability
is not particularly limited because the higher the value is, the
higher the heat is generated when the electromagnetic field for
induction heating as described below is applied. In one example,
the upper limit of the relative magnetic permeability may be, for
example, about 300,000 or less.
[0011] The metal may be a conductive metal. In the present
application, the term conductive metal may mean a metal having a
conductivity at 20.degree. C. of about 8 MS/m or more, 9 MS/m or
more, 10 MS/m or more, 11 MS/m or more, 12 MS/m or more, 13 MS/m or
more, or 14.5 MS/m, or an alloy thereof. The upper limit of the
conductivity is not particularly limited, and for example, may be
about 30 MS/m or less, 25 MS/m or less, or 20 MS/m or less.
[0012] In the present application, the metal having the relative
magnetic permeability and conductivity as above may also be simply
referred to as a conductive magnetic metal.
[0013] By applying the conductive magnetic metal, sintering can be
more effectively performed when the induction heating process to be
described below proceeds. Such a metal can be exemplified by
nickel, iron or cobalt, and the like, but is not limited
thereto.
[0014] The metal component may comprise, if necessary, a second
metal different from the conductive magnetic metal together with
the metal. In this case, the metal foam may be formed of a metal
alloy. As the second metal, a metal having the relative magnetic
permeability and/or conductivity in the same range as the
above-mentioned conductive magnetic metal may also be used, and a
metal having the relative magnetic permeability and/or conductivity
outside the range may be used. In addition, the second metal may
also comprise one or two or more metals. The kind of the second
metal is not particularly limited as long as it is different from
the applied conductive magnetic metal, and for example, one or more
metals, different from the conductive magnetic metal, of copper,
phosphorus, molybdenum, zinc, manganese, chromium, indium, tin,
silver, platinum, gold, aluminum or magnesium, and the like may be
applied, without being limited thereto.
[0015] The ratio of the conductive magnetic metal in the metal
component is not particularly limited. For example, the ratio may
be adjusted so that the ratio may generate an appropriate Joule
heat upon application of the induction heating method to be
described below. For example, the metal component may comprise 30
wt % or more of the conductive magnetic metal based on the weight
of the total metal component. In another example, the ratio of the
conductive magnetic metal in the metal component may be about 35 wt
% or more, about 40 wt % or more, about 45 wt % or more, about 50
wt % or more, about 55 wt % or more, 60 wt % or more, 65 wt % or
more, 70 wt % or more, 75 wt % or more, 80 wt % or more, 85 wt % or
more, or 90 wt % or more. The upper limit of the conductive
magnetic metal ratio is not particularly limited, and may be, for
example, less than about 100 wt %, or 95 wt % or less. However, the
above ratios are exemplary ratios. For example, since the heat
generated by induction heating due to application of an
electromagnetic field can be adjusted according to the strength of
the electromagnetic field applied, the electrical conductivity and
resistance of the metal, and the like, the ratio can be changed
depending on specific conditions.
[0016] The metal component forming the green structure may be in
the form of powder. For example, the metals in the metal component
may have an average particle diameter in a range of about 0.1 .mu.m
to about 200 .mu.m. In another example, the average particle
diameter may be about 0.5 .mu.m or more, about 1 .mu.m or more,
about 2 .mu.m or more, about 3 .mu.m or more, about 4 .mu.m or
more, about 5 .mu.m or more, about 6 .mu.m or more, about 7 .mu.m
or more, or about 8 .mu.m or more. In another example, the average
particle diameter may be about 150 .mu.m or less, 100 .mu.m or
less, 90 .mu.m or less, 80 .mu.m or less, 70 .mu.m or less, 60
.mu.m or less, 50 .mu.m or less, 40 um or less, 30 .mu.m or less,
or 20 .mu.m or less. As the metal in the metal component, one
having different average particle diameters may also be applied.
The average particle diameter can be selected from an appropriate
range in consideration of the shape of the desired metal foam, for
example, the thickness or porosity of the metal foam, and the like,
which is not particularly limited.
[0017] The green structure may be formed using a slurry comprising
first and second solvents together with the metal component
comprising the metal.
[0018] As the first and second solvents, those having different
dielectric constants can be applied. In one example, as the first
solvent, one having a dielectric constant of 20 or more may be
used, and as the second solvent, one having a dielectric constant
of 15 or less may be used. In this specification, the dielectric
constant may be a dielectric constant measured at any one
temperature in a range of about 20.degree. C. to 25.degree. C. If
two kinds of solvents having different dielectric constants are
mixed and used, it is possible to form an emulsion, whereby a pore
structure can be formed by this emulsion.
[0019] In order to increase formation efficiency of the pore
structure, the first and second solvents may be selected so that a
ratio (D1/D2) of a dielectric constant (D1) of the first solvent to
a dielectric constant (D2) of the second solvent is in a range of 5
to 100. In another example, the ratio (D1/D2) may be about 90 or
less, about 80 or less, about 70 or less, about 60 or less, or
about 50 or less.
[0020] The specific dielectric constant range of the first solvent
and the second solvent is not particularly limited as long as it
satisfies the above content.
[0021] In one example, the dielectric constant of the first solvent
may be in the range of 20 to 100. In another example, the
dielectric constant of the first solvent may be about 25 or more,
or about 30 or more. Also, in another example, the dielectric
constant of the first solvent may be about 95 or less, about 90 or
less, or about 85 or less.
[0022] Such a first solvent may be exemplified by, for example,
water, an alcohol such as a monohydric alcohol having 1 to 20
carbon atoms, acetone, N-methylpyrrolidone, N,N-dimethylformamide,
acetonitrile, dimethylacetamide, dimethyl sulfoxide or propylene
carbonate, and the like, but is not limited thereto.
[0023] The dielectric constant of the second solvent may be in the
range of, for example, 1 to 15. In another example, the dielectric
constant of the second solvent may be about 13 or less, about 11 or
less, about 9 or less, about 7 or less, or about 5 or less.
[0024] Such a second solvent may be exemplified by an alkane having
1 to 20 carbon atoms, an alkyl ether having an alkyl group having 1
to 20 carbon atoms, pyridine, ethylene dichloride, dichlorobenzene,
trifluoroacetic acid, tetrahydrofuran, chlorobenzene, chloroform or
toluene, and the like, but is not limited thereto.
[0025] The ratio of each component in the slurry as above may be
appropriately adjusted, which is not particularly limited.
[0026] For example, the metal component in the slurry may have a
ratio in a range of 100 to 300 parts by weight relative to 100
parts by weight of the total weight of the first and second
solvents. In another example, the ratio may be about 290 parts by
weight or less, about 250 parts by weight or less, about 200 parts
by weight or less, about 150 parts by weight or less, or about 120
parts by weight or less, and in another example, it may be about
110 parts by weight or more, or about 120 parts by weigh or
more.
[0027] In addition, the ratio of the first and second solvents in
the slurry may be adjusted so that relative to 100 parts by weight
of any one solvent of the first and second solvents, the part by
weight of the other solvent is in a range of about 0.5 to 10 parts
by weight. In another example, the ratio may be about 9 parts by
weight or less, about 8 parts by weight or less, about 7 parts by
weight or less, about 6 parts by weight or less, about 5 parts by
weight or less, about 4 parts by weight or less, or about 3 parts
by weight or less, and in one example, it may be about 1 part by
weight or more, about 1.5 parts by weight or more, or about 2 parts
by weight or more. For example, the weight ratio of the second
solvent, relative to 100 parts by weight of the first solvent in
the slurry, may be within the above range, or the weight ratio of
the first solvent, relative to 100 parts by weight of the second
solvent, may be within the above range.
[0028] The slurry may further comprise a binder, if necessary. The
kind of the binder is not particularly limited, and may be
appropriately selected depending on the kind of the metal component
or the solvents, and the like applied at the time of producing the
slurry. For example, the binder may be exemplified by alkyl
cellulose having an alkyl group having 1 to 8 carbon atoms such as
methyl cellulose or ethyl cellulose, polyalkylene carbonate having
an alkylene unit having 1 to 8 carbon atoms such as polypropylene
carbonate or polyethylene carbonate, or a polyvinyl alcohol-based
binder such as polyvinyl alcohol or polyvinyl acetate, and the
like, but is not limited thereto.
[0029] For example, in the slurry, the binder may be included at a
ratio of about 10 to 500 parts by weight relative to 100 parts by
weight of the above-described metal component. In another example,
the ratio may be about 450 parts by weight or less, about 400 parts
by weight or less, about 350 parts by weight or less, about 300
parts by weight or less, about 250 parts by weight or less, about
200 parts by weight or less, about 150 parts by weight or less,
about 100 Parts by weight or less, or about 50 parts by weight or
less.
[0030] The slurry may also comprise, in addition to the
above-mentioned components, known additives which are additionally
required.
[0031] The method of forming the green structure using the slurry
as above is not particularly limited. In the field of manufacturing
metal foams, various methods for forming the green structure are
known, and in the present application all of these methods can be
applied. For example, the green structure may be formed by holding
the slurry in an appropriate template, or by coating the slurry in
an appropriate manner.
[0032] The shape of such a green structure is not particularly
limited as it is determined depending on the desired metal foam. In
one example, the green structure may be in the form of a film or
sheet. For example, when the structure is in the form of a film or
sheet, the thickness may be 5,000 .mu.m or less, 3,500 .mu.m or
less, 2,000 .mu.m or less, 1000 .mu.m or less, 800 .mu.m or less,
700 .mu.m or less, or 500 .mu.m or less. Metal foams have generally
brittle characteristics due to their porous structural features, so
that there are problems that they are difficult to be manufactured
in the form of films or sheets, particularly thin films or sheets,
and are easily broken even when they are made. However, according
to the method of the present application, it is possible to form a
metal foam having pores uniformly formed inside and excellent
mechanical properties as well as a thin thickness.
[0033] The lower limit of the structure thickness is not
particularly limited. For example, the film or sheet shaped
structure may have a thickness of about 10 .mu.m or more, 50 .mu.m
or more, or about 100 .mu.m or more.
[0034] The metal foam can be manufactured by sintering the green
structure formed in the above manner. In this case, a method of
performing the sintering for producing the metal foam is not
particularly limited, and a known sintering method can be applied.
That is, the sintering can proceed by a method of applying an
appropriate amount of heat to the green structure in an appropriate
manner.
[0035] As a method different from the existing known method, in the
present application, the sintering can be performed by an induction
heating method. That is, as described above, the metal component
comprises the conductive magnetic metal having the predetermined
magnetic permeability and conductivity, and thus the induction
heating method can be applied. By such a method, it is possible to
smoothly manufacture metal foams having excellent mechanical
properties and whose porosity is controlled to the desired level as
well as comprising uniformly formed pores.
[0036] Here, the induction heating is a phenomenon in which heat is
generated from a specific metal when an electromagnetic field is
applied. For example, if an electromagnetic field is applied to a
metal having a proper conductivity and magnetic permeability, eddy
currents are generated in the metal, and Joule heating occurs due
to the resistance of the metal. In the present application, a
sintering process through such a phenomenon can be performed. In
the present application, the sintering of the metal foam can be
performed in a short time by applying such a method, thereby
ensuring the processability, and at the same time, the metal foam
having excellent mechanical strength as well as being in the form
of a thin film having a high porosity can be produced.
[0037] Thus, the sintering process may comprise a step of applying
an electromagnetic field to the green structure. By the application
of the electromagnetic field, Joule heat is generated by the
induction heating phenomenon in the conductive magnetic metal of
the metal component, whereby the structure can be sintered. At this
time, the conditions for applying the electromagnetic field are not
particularly limited as they are determined depending on the kind
and ratio of the conductive magnetic metal in the green structure,
and the like. For example, the induction heating can be performed
using an induction heater formed in the form of a coil or the like.
In addition, the induction heating can be performed, for example,
by applying a current of 100 A to 1,000 A or so. In another
example, the applied current may have a magnitude of 900 A or less,
800 A or less, 700 A or less, 600 A or less, 500 A or less, or 400
A or less. In another example, the current may have a magnitude of
about 150 A or more, about 200 A or more, or about 250 A or
more.
[0038] The induction heating can be performed, for example, at a
frequency of about 100 kHz to 1,000 kHz. In another example, the
frequency may be 900 kHz or less, 800 kHz or less, 700 kHz or less,
600 kHz or less, 500 kHz or less, or 450 kHz or less. In another
example, the frequency may be about 150 kHz or more, about 200 kHz
or more, or about 250 kHz or more.
[0039] The application of the electromagnetic field for the
induction heating can be performed within a range of, for example,
about 1 minute to 10 hours. In another example, the application
time may be about 9 hours or less, about 8 hours or less, about 7
hours or less, about 6 hours or less, about 5 hours or less, about
4 hours or less, about 3 hours or less, about 2 hours or less,
about 1 hour or less, or about 30 minutes or less.
[0040] The above-mentioned induction heating conditions, for
example, the applied current, the frequency and the application
time, and the like may be changed in consideration of the kind and
the ratio of the conductive magnetic metal, as described above.
[0041] The sintering of the green structure may be carried out only
by the above-mentioned induction heating, or may also be carried
out by applying an appropriate heat, together with the induction
heating, that is, the application of the electromagnetic field, if
necessary.
[0042] The present application also relates to a metal foam. The
metal foam may be one manufactured by the above-mentioned method.
Such a metal foam may comprise, for example, at least the
above-described conductive magnetic metal. The metal foam may
comprise, on the basis of weight, 30 wt % or more, 35 wt % or more,
40 wt % or more, 45 wt % or more, or 50 wt % or more of the
conductive magnetic metal. In another example, the ratio of the
conductive magnetic metal in the metal foam may be about 55 wt % or
more, 60 wt % or more, 65 wt % or more, 70 wt % or more, 75 wt % or
more, 80 wt % or more, 85 wt % or more, or 90 wt % or more. The
upper limit of the ratio of the conductive magnetic metal is not
particularly limited, and may be, for example, less than about 100
wt % or 95 wt % or less.
[0043] The metal foam may have a porosity in a range of about 40%
to 99%. As mentioned above, according to the method of the present
application, porosity and mechanical strength can be controlled,
while comprising uniformly formed pores. The porosity may be 50% or
more, 60% or more, 70% or more, 75% or more, or 80% or more, or may
be 95% or less, or 90% or less.
[0044] The metal foam may also be present in the form of thin films
or sheets. In one example, the metal foam may be in the form of a
film or sheet. The metal foam of such a film or sheet form may have
a thickness of 2,000 .mu.m or less, 1,500 .mu.m or less, 1,000
.mu.m or less, 900 .mu.m or less, 800 .mu.m or less, 700 .mu.m or
less, 600 .mu.m or less, 500 .mu.m or less, 400 .mu.m or less, 300
.mu.m or less, 200 .mu.m or less, 150 .mu.m or less, about 100
.mu.m or less, about 90 .mu.m or less, about 80 .mu.m or less,
about 70 .mu.m or less, about 60 .mu.m or less, or about 55 .mu.m
tm or less. For example, the film or sheet shaped metal foam may
have a thickness of about 10 .mu.m or more, about 20 .mu.m or more,
about 30 .mu.m or more, about 40 .mu.m or more, about 50 .mu.m or
more, about 100 .mu.m or more, about 150 .mu.m or more, about 200
.mu.m or more, about 250 .mu.m or more, about 300 .mu.m or more,
about 350 .mu.m or more, about 400 .mu.m or more, about 450 .mu.m
or more, or about 500 .mu.m or more.
[0045] Such metal foams can be utilized in various applications
where a porous metal structure is required. In particular,
according to the method of the present application, it is possible
to manufacture a thin film or sheet shaped metal foam having
excellent mechanical strength as well as the desired level of
porosity, as described above, thus expanding applications of the
metal foam as compared to the conventional metal foam.
Advantageous Effects
[0046] The present application can provide a method for
manufacturing a metal foam, which is capable of forming a metal
foam comprising uniformly formed pores and having excellent
mechanical properties as well as the desired porosity, and a metal
foam having the above characteristics. In addition, the present
application can provide a method capable of forming a metal foam in
which the above-mentioned physical properties are ensured, while
being in the form of a thin film or sheet, and such a metal
foam.
BRIEF DESCRIPTION OF DRAWINGS
[0047] FIGS. 1 to 3 are SEM photographs of metal foams formed in
Examples.
MODE FOR INVENTION
[0048] Hereinafter, the present application will be described in
detail by way of examples and comparative examples, but the scope
of the present application is not limited to the following
examples.
Example 1
[0049] Methyl cellulose and hydropropyl methyl cellulose as
polymeric binders are mixed with 35.0 g of water (dielectric
constant at 20.degree. C.: about 80) as a first solvent in amounts
of 1.9 g and 3.6 g, respectively, stirred and dissolved. After the
dissolution is completed, 54.0 g of nickel powder (having
conductivity of about 14.5 MS/m, relative magnetic permeability of
about 600 and average particle diameter of about 10 to 20 .mu.m),
2.7 g of a surfactant and 2.0 g of ethylene glycol are sequentially
added and stirred. Thereafter, 0.8 g of pentane (dielectric
constant at 20.degree. C.: about 1.84) to be used as a foaming
agent is added and stirred.
[0050] The sample prepared through the above process is bar-coated
on a silicon nitride plate to a thickness of 0.5 mm, heated to
40.degree. C. in a space having a humidity of 80% or more and
foamed for 10 minutes. Thereafter, it was heated at 80.degree. C.
under a humidity of 60% or less for 30 minutes and the solvent was
dried to form a green structure (film). An electromagnetic field
was then applied to the green structure with a coil-type induction
heater while purging with hydrogen/argon gas to form a reducing
atmosphere. The electromagnetic field was formed by applying a
current of about 350 A at a frequency of about 380 kHz, and the
electromagnetic field was applied for about 3 minutes. After the
application of the electromagnetic field, the sintered green
structure was cleaned to produce a sheet having a thickness of
about 1.5 mm in the form of a film. The produced sheet had a
porosity of about 91%. FIG. 1 is an SEM photograph of the produced
sheet.
Example 2
[0051] A sheet having a thickness of about 1.7 mm was produced in
the same manner as in Example 1, except that as the second solvent,
hexane (dielectric constant at 20.degree. C.: about 1.88) was used
instead of pentane. The produced sheet had a porosity of about 94%.
FIG. 2 is an SEM photograph of the produced sheet.
Example 3
[0052] A sheet having a thickness of about 0.7 mm was produced in
the same manner as in Example 2, except that as the first solvent,
NMP (N-Methylpyrrolidone) (dielectric constant at 25.degree. C.:
about 32.2) was used instead of water. The produced sheet had a
porosity of about 62%. FIG. 3 is an SEM photograph of the produced
sheet.
Example 4
[0053] A sheet having a thickness of about 1.1 mm was produced in
the same manner as in Example 2, except that as the second solvent,
ethyl ether (dielectric constant at 20.degree. C.: about 4.33) was
used instead of pentane. The produced sheet had a porosity of about
81%.
Comparative Example 1
[0054] A sheet was produced in the same manner as in Example 1,
except that the second solvent was not applied and the weight ratio
(W:MC) of water (W) to methyl cellulose (MC) was 95:5. The produced
sheet was very brittle and easily broken, and thus the tensile
strength could not be measured, and the pores were also formed very
non-uniformly.
Comparative Example 2
[0055] A sheet was produced in the same manner as in Example 3,
except that the second solvent was not applied and the weight ratio
(NMP:MC) of NMP and methyl cellulose (MC) was 95:5. The produced
sheet was very brittle and easily broken, and thus the tensile
strength could not be measured, and the pores were also formed very
non-uniformly.
* * * * *